Since low initial cost and reduced running cost are usually essential requirements for treating municipal wastes, it is desirable that the furnace used be directly heated with the combustible gases derived from the processor. To assure maximum combustion temperature, air or like gas must be preheated prior to combustion in sufficient volumes to burn the required gas flow in order to treat the volumes of waste being processed in the desired time period.
With a system in which air and/or like gass are fed to a high-temperature furnace bed of combustible carbonaceous material from below to effect combustion to cause the resulting combustion gas to flow upward, dust of the waste and ash are exposed to, and scattered upward by, a large quantity of combustion gas flowing at a high speed, with the result that the dust will be released from the furnace as entrained in the combustion gas. The exhaust gas is therefore very likely to cause secondary pollution or clog up, damage or overheat the exhaust duct.
Conversely with another system in which the gas for combustion is fed to the high-temperature furnace bed from above to cause the resulting combustion gas to flow downward, the water contained in the waste will flow down along with the combustion gas, giving a reduced temperature to the lower portion of the bed. Additionally, the carbon dioxide and water resulting from the combustion of the waste, or the water initially contained in the waste also flows downward with the combustion gas undergoing a reduction reaction with the carbon component of the combustible carbonaceous material in the lower portion of the furnace bed to absorb the ambient heat and eventually reducing the temperature of the lower portion of the bed. At a reduced temperature, the product will block up and will not be run off from the furnace smoothly.
Secondary pollution and other objections due to the exhaust gas could be prevented with use of a secondary combustion chamber or combustion promoting device, or by returning the exhaust gas into the furnace, while an additional heater, if provided for the lower portion of the bed, would be useful for keeping this portion at the desired high temperature. Such means, however, would render the furnace construction complex and result in an increase in the initial cost as well as in the running cost due to damage to the structure.
U.S. Pat. No. 4,029,026 of Normantas discloses pollution-free incinerators in which slow, starved oxygen combustion is commenced at the base of a primary combustion chamber which utilizes gases generated from the initial combustion area to fire the primary combustion chamber and to burn gases generated therefrom.
U.S. Pat. No. 4,376,373 of Weber et al relates to a system for incinerating scrap automobiles whereby waste oil volatile compounds are collected and heat from an incinerator is used to break down waste oil in a cracking tower.
U.S. Pat. No. 4,452,152 of John et al discloses an incinerator steam generation system which utilizes heat derived from municipal waste to produce steam for steam boiler, electrical generating facilities, heating facility for industrial plants and the like.
U.S. Pat. No. 4,253,405 of Cottrell et al relates to a system for incinerating combustible solid waste and for resolving ash and heat from streams of by-products of combustion.
U.S. Pat. No. 4,437,419 of Karl R. Hertel, which is incorporated herein by reference, discloses a system for incinerating waste and reclaiming resources in a separate output stream.